I've had my HTC M8 for a few weeks now but recently I've started hearing this weird "bloop" notification type of sound. It's very soft - not as loud as regular notifications and almost sounds like it's due to a connection maybe?
Every time I heard it I look at my screen to see if my phone is alerting me to something but I can't ever find anything.

On my old HTC it would make a sound every time I would lose or re-enter a service area (inside the mall there must be a dead spot) but it was a normal notification sound - but the frequency reminds me of this.

I do have my data hooked up to wifi at work (right now) and at home and I can't say I've ever heard it when I'm not on wifi but really the only times I'm not on wifi are when I'm not at home or work and during those times I likely wouldn't hear it because it would be in my purse.

I used to hear it every once in awhile but just this morning I've heard it a handful of times.

I'm just hoping this is a normal noise?